The invention relates to a filter for filtering liquids, in particular a transmission oil filter. However, the invention is useable also in connection with filtration of lubricant oil, hydraulic oil, or compressor oil.
Transmission oil filters are known that have a fiberglass layer that is covered on both faces with a spunbond nonwoven. The spunbond nonwoven improves handling of the fiberglass layer, for example, in the manufacturing process of the filter.
Multi-layer filters for the filtration of liquids are known as, for example, disclosed in European patent 1 035 902. A melt blown nonwoven is disclosed that is provided at the downstream side with a layer of cellulose-containing filter paper.
In connection with air filtration, DE 100 133 15 discloses that fiberglass media release fiberglass pieces into the area of the purified medium. Therefore, this reference recommends that fiberglass media should be replaced with other types of filter materials. Such a release of fiberglass pieces can also be observed in connection with liquid filtration where fiberglass media are used that are covered or lined with spunbond nonwoven.
It is an object of the present invention to prevent or to reduce the release of fiberglass or fiberglass pieces into the filtered fluid in connection with a transmission oil filter comprising a filtration layer of fiberglass medium.